H&K developed the UMP to be their next generation submachine gun and the successor of their long standing MP5. They built it with with a space-age polymer body and improved mechanics to better suit their new SMG for the modern operator. They also took a radical departure from the traditional 9mm round and also chambered their UMP for the hard hitting .40 S&W and .45 ACP rounds making it one of the most powerful submachine guns on the planet.